Sustainability is something's ability to be sustained. (Similar to maintained, kept, continued). Often these days we hear about 'sustainability' in resources and staying 'sustainable.' This refers to spending and using things in a manner in which we will never run out of those things. Oil for instance is not a sustainable resource. It is in limited supply and once it's gone, it's gone. When we rely on oil, we are not being sustainable. "For the company to be sustainable, we must reduce the production costs." In this sentence, the company being sustainable is a reference to spending versus income. A company must make more than it spends in order to stay alive. In this situation, production costs are too high, so the company can't be sustainable unless it can lower those costs.

Sustainability means the capacity to endure. The word sustainability is derived from the Latin sustinere (tenere, to hold; sus, up). Dictionaries provide more than ten meanings for sustain, the main ones being to “maintain", "support", or "endure”.